“Cannabinoids are a group of terpenophenolic compounds present in Cannabis (”Cannabis sativa”) and occur naturally in the nervous and immune systems of animals.

The broader definition of cannabinoids refers to a group of substances that are structurally related to tetrahydrocannabinol (THC) or that bind to cannabinoid receptors.

The chemical definition encompasses a variety of distinct chemical classes: the classical cannabinoids structurally related to THC, the nonclassical cannabinoids, the aminoalkylindoles, the eicosanoids related to the endocannabinoids, 1, quinolines and arylsulphonamides, and additional compounds that do not fall into these standard classes but bind to cannabinoid receptors.

The term ”cannabinoids” also refers to a unique group of secondary metabolites found in the cannabis plant, which are responsible for the plant’s peculiar pharmacological effects.

At the present time, there are three general types of cannabinoids: ”phytocannabinoids” occur uniquely in the cannabis plant; ”endogenous cannabinoids” are produced in the bodies of humans and other animals; and ”synthetic cannabinoids” are similar compounds produced in a laboratory.”

http://www.news-medical.net/health/Cannabinoids-What-are-Cannabinoids.aspx